+type StringSet map[string]struct{}
+
+// UnmarshalJSON handles old config files that provide an array of
+// instance types instead of a hash.
+func (ss *StringSet) UnmarshalJSON(data []byte) error {
+ if len(data) > 0 && data[0] == '[' {
+ var arr []string
+ err := json.Unmarshal(data, &arr)
+ if err != nil {
+ return err
+ }
+ if len(arr) == 0 {
+ *ss = nil
+ return nil
+ }
+ *ss = make(map[string]struct{}, len(arr))
+ for _, t := range arr {
+ (*ss)[t] = struct{}{}
+ }
+ return nil
+ }
+ var hash map[string]struct{}
+ err := json.Unmarshal(data, &hash)
+ if err != nil {
+ return err
+ }
+ *ss = make(map[string]struct{}, len(hash))
+ for t, _ := range hash {
+ (*ss)[t] = struct{}{}
+ }
+
+ return nil
+}
+